My nudes are being sent around?

[Francheska]

So recently I got involved with a guy from another school who I knew through a few friends and we began exchanging pictures on snapchat. At first it was all friendly and casual, but after a while he began sending me shirtless pictures of himself and asked me to "return the favour". I didn't want to send him a topless picture of myself so instead I send a picture of myself in a tank top with a little cleavage showing (but it wasn't too revealing). I sent him others similar to that but after a while I found out that he had been screenshotting my snaps (they didn't even send me a screenshot notification!) and that he had been sending them to numerous people in his year saying I was a slut and calling me names. When I asked some of his friends if they'd seen the pictures, all of them lied about it and denied that they'd ever seen them, except for one of them who was honest and showed me screenshots of stuff they
d said about me. After this, I started getting harassed by text message and facebook. One of the guys tagged me in a picture that said "tag the biggest slut on your friends list". I was really angry and confused because I didn't think the pictures I'd sent were that revealing and to be fair a lot of those guys were friends with other girls who had done much worse things that I had, but for some reason I was the one who got picked on.
I even went to my school year advisor to get help and to get him in trouble, but they didn't do anything for me since they claimed that we had both done something wrong and that if it went to the police I would get in trouble as well for indecent exposure.

So my question is, what do you guys think I should do? I don't want to be passive and let this slide because I believe the guy should at least get in some trouble for this and have consequences for his actions.

(P.S Title is slightly misleading - sorry for that)
Edit:
This guy does not go to my school and the photos aren't completely naked - just cleavage showing
Paul please stop downvoting everyone's answers just because yours was downvoted deservingly

[Under Siege]

This is harassment, contact your school and get this punk expelled.

[JP]

There is really nothing you can do at this point, you didn't send any nudes, so you can't get in trouble for indecent exposure or any of that BS, so if you really deem it necessary, the police would be a viable option, though a bit drastic and unnecessarily.

[Menchitah]

You can always screenshot the message he sent you (him asking for your picture) if you can. It happened to a friend of mines before. She screenshot it and sent it to the school and they expelled the guy